A heat trace system (HTS) is basically a device that distributes alternating current (AC) electricity to one or more heat trace sections where heating elements maintain or raise the temperature of equipment (e.g. insulated pipes, vessels, etc.).
Heating prevents equipment from freezing by replacing heat lost to the atmosphere. If the heat replaced matches the heat lost due to falling ambient temperatures, the equipment temperature remains constant. An ambient temperature thermocouple sensor together with heat trace thermocouple sensors may be used to control equipment temperature by activating their heat trace sections before the equipment freezes. 40° F. is the usual standard for turning on heat.
Since heat trace systems require alternating current, they are well adapted for use near commercial AC power outlets. However there is also a need for heat trace systems at remote locations where there is no commercial source of AC. The present invention provides a remote HTS powered by renewable sources of AC electrical power that is cost-effective, reliable, environmentally friendly.
Combustion engines generators are well-known in the art, and, while they produce sufficient DC for heat trace systems, they require fueling, constant maintenance, and may be environmentally unacceptable.
Solar panels may also be used to produce DC electricity, but solar panels generate electricity only when they are exposed to sunlight, and the number required to power an effective HTS would be expensive.
Aerogenerators (wind turbines) produce sufficient DC electricity for an effective HTS when wind velocities are within a certain range, but they produce no electricity when the wind velocity is too low or too high.
The present invention provides a reliable, inexpensive, environmentally friendly HTS for use in remote locations by combining the cost-effectiveness of aerogenerators with non-polluting solar power, and controlling the distribution of the energy produced with a novel homeostatic control mechanism.
There is nothing new about combining solar and wind power to generate DC electricity. Hickey, U.S. Pat. No. 5,254,876 discloses a combination solar and wind powered generator with a plurality of light sensitive cells in spiral vanes. Whitworth, U.S. Pat. No. 7,008,171 discloses a plurality of modified Savonius rotors which may be coated with photo voltaic cell material and have a cone-shaped solar collector on top for additional energy production. Kashyap, U.S. Pat. No. 7,045,702 discloses an electrical generator comprising a windmill with aerodynamic blades provided with solar panels. Gilbert, U.S. Pat. No. 7,453,167 disclose a wind turbine with solar panels mounted on the surfaces of the turbine such that the energy output is from both sources. Suzuki et al., U.S. Pat. No. 7,449,798 discloses a co-generated power supply using wind and solar energy integrated with a commercial power source for a voltage and load-leveling constant power device. Semenovitch, RU 2350847 discloses a device that includes a photovoltaic module, a wind power plant and a micro hydro-power plant to enhance the efficiency of an in-well heat supply system.
The present invention is distinct from the prior art in may ways, including that none of these wind/solar devices provide controlled AC input to sections of a multi-sectioned heat trace system, with energy distribution when generation from wind is low.
There is a need for heat trace systems at remote oil and gas well sites and pipelines to protect pipelines and equipment from freezing, to increase or maintain fluid viscosity and flow in pipelines, and/or to enhance production. Yewell, U.S. Pat. No. 6,032,732 re-routes engine coolant from a pumper engine to a heat tracing loop that protects a well head assembly from freezing. McClung, U.S. Pat. No. 6,338,381 disclose a system that transfers heat between an earth conduit or loop and a pipeline, rig or wellhead, thereby heating or cooling the pipeline, rig or wellhead. Beida, U.S. Pat. No. 6,776,227 discloses a method for preventing freezing of wellhead equipment utilizing radiant heat from a flameless heater to heat fluid that is circulated to the equipment. Bourgeois et al., U.S. Pub. No. 2009/0119073 & W.O. Pub. No. 2009/055545 disclose a design and method for finding potential freeze spots in pipe systems. Finally, Hiroyuki, JP 2000,009,879 and Yoshimasa et al., JP 2004,103,267 provide a control device for a HTS using a commercial utility supply.
Thus, prior art heat trace systems used at remote oil and gas wells are generally powered by a commercial utility source, a combustion engine generator or a heat source that is not electrical. None of these heat trace systems is powered by electricity.
There are a number of reasons why solar electrical generators are not widely used to generate electricity for heat trace systems at remote oil and gas wells. One is because the solar panels needed to power heat traces of a practical size are expensive. Another is because they produce no energy during night, and they can be unreliable in locations where sunlight is inadequate. Yet other reasons are because smaller solar panels have insufficient power for longer heat trace sections. Yet another reason is because solar panel control systems are unable to monitor multiple sections areas for heat tracing, and have no means for maximizing power as required by the actual conditions at the well. For example, the heat trace system disclosed by Squire, CA 2497375 uses a timing relay to maintain a fifty percent (one hour on, one hour off) “duty cycle” to reduce the size of the solar panels. Even so, CA '375's 20 watt/ft heat trace produces only 7 watt/ft of heat that can be run no farther than five feet. Moreover, the HTS in CA '375 lacks a means for maximizing power utilization, nor can it monitor multiple areas for heat tracing.
Likewise, there are a number of reasons why wind-powered electrical generators are not widely used to generate electricity for heat trace systems at remote well sites. One is because they are unreliable without backup at remote locations where wind velocities may be inadequate or too great. Another is because they a lack means of obtaining a constant flow of heat trace track cable and the ability to monitor the area being heat traced or the ability to distribute heat when stored energy is low. For example, in the heat trace system disclosed by Qing-Wu et al., CN 201083112, a hyperbola negative-pressure duplex windmill is connected directly to heating cables via an asynchronous device that converts the mechanical energy into electricity and a transformer that converts three-phase voltage into single-phase. If there is any excess energy, it is stored as heat in oil wells and released later when the wind velocity is low.
There is therefore a need for a simple, cost-effective, and environmentally friendly combined wind and solar-powered generator that reliably generates sufficient energy for heat trace systems used in oil and gas recovery systems and pipelines operating in remote locations without a source of commercial electrical power.